President Joe Biden on Thursday announced the United States is buying 10 million courses of Pfizer's Covid-19 treatment pill, in a $5.3 billion deal he touted as "critical" to fighting the pandemic.

Pfizer applied this week for US emergency use authorization for its Paxlovid antiviral pill, shown to be highly effective in preventing hospitalization and death among high-risk patients.

While the deal hinges on the treatment's approval by the Food and Drug Administration, Biden said he had taken "immediate steps to secure enough supply for the American people."

"Today, I'm announcing that we have purchased 10 million treatment courses of the Pfizer antiviral Covid-19 pill, with delivery starting at the end of this year and across 2022," he said in a statement, adding that the treatments would be "easily accessible and free."

While emphasizing that widely-available vaccines remain America's "strongest tool" in the fight against Covid-19, Biden said the antiviral "treatment could prove to be another critical tool in our arsenal that will accelerate our path out of the pandemic."

Among newly-infected high risk patients treated within three days of the onset of symptoms, Pfizer's pill has been shown to cut hospitalization or death by nearly 90 percent.

Pfizer separately announced the $5.3 billion deal, subject to approval from regulators, early Thursday.

Pfizer will begin delivering Covid-19 treatments to the US government later this year and through the end of 2022
Alaska's COVID-19 treatment supply is running low. Pfizer via AFP / Handout

The US government announced in June it was investing $3 billion to accelerate the discovery, development and manufacturing of antiviral medicines.

The United States is also buying 3.1 million courses of an antiviral pill developed by Merck, called Molnupiravir, which is awaiting an FDA green light.

Pfizer's Paxlovid is a combination of a new molecule, PF-07321332, and HIV antiviral ritonavir. Both belong to a class of antivirals called "protease inhibitors," which block the action of an enzyme critical to viral replication.

A treatment course consists of one pill every 12 hours for five days.

"We were thrilled with the recent results of our Phase 2/3 interim analysis, which showed overwhelming efficacy of Paxlovid... and are pleased the US government recognizes this potential," Pfizer Chairman and chief executive Albert Bourla said in its statement.

"It is encouraging to see a growing understanding of the valuable role that oral investigational therapies may play in combatting Covid-19, and we look forward to continuing discussions with governments around the world to help ensure broad access for people everywhere."

Pills are easier to make than vaccines, do not require a cold chain for delivery and can be self-administered by the patient.

Pfizer has entered into advance purchase agreements for its antiviral pill with several other countries and has initiated bilateral outreach to approximately 100 nations around the world, declaring itself committed to working on "equitable access" for the treatment at an affordable price.

It announced a deal Tuesday with the UN-backed Medicines Patent Pool (MPP) to sub-license production to generic manufacturers for supply in 95 low- and middle-income countries, covering around 53 percent of the world's population.

Coronavirus